Dispensers are known for dispensing fluids from bottles which are enclosed other than for an opening through which the fluid is to be dispensed. Various arrangements arise for relieving vacuum which may develop within the bottle. A disadvantage arises in prior art devices that to maintain the bottle in the shape and appearance that occurs when full, the bottle needs to be provided with sufficient strength to resist collapse when a vacuum condition may be developed within the interior of the bottle.
One-way vacuum release valves are known which provide in the condition that a substantial vacuum is developed within a bottle, that the one-way relief valve may permit air to enter the bottle towards relieving the vacuum within the bottle. Such one-way relief valves suffer the disadvantage that generally a relatively substantial vacuum needs to be developed in the bottle for the air valve to be effective and that the vacuum which is created in the bottle typically requires the bottle to at least be somewhat resistant to collapse under vacuum conditions.
Fluid dispensers are known in which the fluid is contained within a collapsible bottle or a flexible plastic bag. The use of such collapsible bottles and collapsible bags suffer the disadvantage that during the collapse, the bottle or bag may collapse in a manner that it traps fluid in portions of the bottle which cannot then be dispensed and is wasted. Additionally, the collapse of the bottle or bag can provide the bottle or bag with an unsightly appearance.